title: Hydrogen-1 nuclear magnetic resonance study of the complexes of two diastereoisomers of folinic acid with dihydrofolate reductase.
abstract: The 1H chemical shifts for the formyl and benzoyl protons of the individual diastereoisomeres of folinic acid bound to dihydrofolate reductase have been measured. For the tightly bound biologically active 6S, alpha S isomer, the "bound" signals were assigned by using transfer of saturation methods. In this case, only one of the two rotameric states of the formyl group in folinic acid (form I) is bound to the enzyme. The H3' and H5' benzoyl protons have identical shifts in the bound state (as do the H2' and H6' protons). This equivalence is attributed to flipping of the benzoyl ring about the N10-C4' and C1'-CO bonds in the bound state. In the case of the biologically inactive 6R, alpha S isomer, both rotameric forms (I and II) bind to the enzyme. The "bound" shifts for the formyl and aromatic protons are different in the complexes with the 6S, alpha S and 6R, alpha S isomers, indicating that the pteridine ring and benzoyl moiety are binding in different environments in their enzyme complexes. The glutamic acid moiety is probably binding at the same site in the two complexes.
mesh_terms: D007780:Lacticaseibacillus casei / Q000201:enzymology; D002955:Leucovorin / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D011485:Protein Binding; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism*
chemical_list: D013762:Tetrahydrofolate Dehydrogenase; D002955:Leucovorin